Process for making metal strip from metal powder



F. V. LENEL May 24, 1960 PROCESS FOR MAKING METAL STRIP FROM METALPOWDER Filed Jan. 23, 1957 INVENTOR /Z/7Z 1 [Awe-4 ATTORNEY Unite StatesI tier being processed. I

to animproved process for controlling the permeabilityandotherlimportant properties across the width of a metal strip formedby roll compacting a metal powder layer inxa continuous operation. Theinvention is especially" useful forIminimizing the variation inproperties and characteristics normally obtained across the width ofrthe metal strip whereby more efiicient utilization of the resultingproduct is-made possible in connection with its various 'applications. 11

1 It has been known for some time that metal powders maybecompacted byrolling to produce a so-called green compact in the form of strip whichis then heat treated or---sintered and, if necessary, re-rolledtodevelop the desired final properties.

I whilerolling orthe powder in accordance with prior artproeeduresresults in the production of strip material which maybegenerally useful-for some applications, a 'serioiisdis'advantage oftenresulting in 'the rejection of considerable amounts of thefinished-product has been thevariation in properties across the width ofthe rolled stocki This variation of properties occurring across thewidth of the strip affecting, for example, the density,

7 porosity and particularly'thepermeability of the material is highlydetrimentalfor many applications where more uniform properties areessential.

atent I The above disadvantages are overcome by this invention whichprovides for controlling the permeability and related properties of rollcompacted metal strip by supplying the roll gap of a set of ordinaryrolls witha continuous layer of loose metal powderof predeterminedprogressively increasing thickness laterally from the center of theloose metal powder layer. When the powder layer of modifiedcross-sectional thickness as'hereinafter described in detail issubjected to roll compacting in the usual manner, the provided increase,in thicknesstoward the lateral extremities enables the productionof'strip'having permeability and other properties which may becontrolled substantially as desired. It is readily apparent that stripof more uniform properties along its entire width may be obtained bycompensating for the spreading tendency in this manner. I I

It is therefore a principal object of this invention to provide animproved process for controlling the permeability across the width'ofmetal strip formed by rolling metal powder in a continuous operation. I

Another object of this invention is to provide a proc- I ess forproducing strip from metal powder of improved I The-permeability ofmetal strip which is a measure of the-amount of a-giverrfluid (includingair) which can be passed through a unit area of strip of equivalentthickness under equivalent conditions of. pr'essureand time is aproperty of prime significance This particular property is especiallyimportant where roll c'ompacted'metal I strip is to find eventualapplication in the manufacture of bearings, filters and transpirationcooled aircraft componentssuch as turbine blades, combustion chambersand deicing' devices. r

I iBasically, the reason for theaforesaid-variation in permeability andother related properties in a metal strip formed by the rolling ofmetalpowders between a set of conventional parallel rolls is the naturaltendency of the powder to spread sideways or laterally under the rollpressure. Because' ofthis-spreading, all too frequently only a certainportion of the metal strip, such as the center portion thereof, asdistinguished from the portions to either side of the'centen'can beutilized for the manufacture of'specific articles therefrom. This is dueto the fact that the desired permeability on either side of the centerdiverges unacceptably far from the specified or average propertiesdesired. Variations of 30% or more in permeabilityare not unusualbetween the center and terminal sections of strip in the absence ofcontrol measures.

-The use of-shaped rolls to provide a differential roll pressure acrossthe width of the strip or, alternatively, roll pairs with cooperatingrecesses and projections to limit the spreading of the-powders have beenpreviously suggested. These solutions are, however, cumbersome at bestinasmuch as theyi'equire a manufacturer to maintain a large inventoryofexpensive rolls which must be exchanged for'anothersuch set of rollswith each and every change in the specifications of the strip to be madeas well as upon changes in the kind or particle size of metal pow:

uniformity with respect to the permeability, density and porosity of thecompacted product. I I

A further object of this invention is to. provide a process forminimizing the'variation of properties of metal tion, it will beunderstood that these advantages and ob- I I jects are also equallyattained in terms of 'eitherdens'ity or porosity of the metal stripwhich are relatedproperties of permeability. The relationship ofdensity, porosity andpermeability can be qualitatively understood in thesensethat permeability is the amountand'size'of inter! connectedporosity, which in turn is a direct function of the particle'size of thepowder and of the extent of compacting or densification of the metalparticles comprising the strip.

The invention will be more clearly understood byreference to theaccompanyingdrawing in which:

Fig. 1 schematically illustrates a side view of a general arrangement ofapparatus incorporating a contoured gate suitable for practicing theinvention, i U r Fig. 2 is a perspectiveview of the control gate in anadjustable mounting at the head of; an inclined feed trough, used forcontinuously'feeding a contoured layer of metal powder to the roll gap,

Fig. 3 is a side view of the control gate, and

Fig. 4 is a sectional view taken along the line 4-4 in Fig. 1 showingthe metal powder layer in contoured form prior to compacting.

Referring now to the drawing, a supply of loose metal powder 10 iscontained in a sloped bottom feed hopper 11 which is fitted withgateguides 12 in which a control gate 13 is slidably supported to permitvertical movement of. the gate in the guides thereby providing an outletapere ture 14 for passage of the powder from the hopper 11 upon a feedtrough 20. I Adjustment of aperture 14 may be made either manually or bymechanical means (not shown) associated with gate lifter 15. Indexingthe vertical movement enables rapid and accuratepositioningiofthecontrol gate and any suitable lockingmeans' may be used for securing theadjustment once the desired position is determined.

' In the embodiment shown in Fig. 2, control gate 13*com-' prises asheet ,metalplate having aflixed along its bottom;

oil edge a shaping or contouring metal blade 16 which is attached to thegate by strap 17 thereby permitting ready changing of the blade wheneverrequired. The lower extremity of blade 16 designated at 18 which definesthe shape of the outlet aperture and which effects the contour ing ofthe loose metal powder layer upon its passage therethrough is preferablybevelled across its entire width to a knife edge most clearly shown inFig. 3. Best results are obtained when the bevelled edge is positionedoutwardly as shown in Fig. 1.

Outlet aperture 14 opens into a feed trough 20 having sides 21 and abottom 22 which is abutting and coextensive with the bottom 23, of thehopper 11. The width of the feed trough should correspond to the widthof the aperture between the inner edges of the guides 12 in order toprevent disruption of the contoured metal powder layer once it isformed. A minimum distance of travel represented by the length of thetrough is of importance for the same reason.

The feed trough 20,-which may be structurally supported in any suitablemanner, conducts and deposits the contoured loose metal powder layer onthe lower of the two cooperating rolls 24 whereupon the powder is drawninto the roll gap 25 by the friction between rolls and powder and iscompacted to a so-called green strip 26 by the roll pressure.

A representative specimen of a layer of loose metal powder which hasbeen passed through an arcuate shaped aperture in accordance with thepresent invention resulting in a controlled distribution of the powderis shown in section in Fig. 4 wherein the layer is characterized by aprogressively increasing thickness from the center line 27 toward theextremities comprising the width of the strip. The difference in heightfrom the center to the extremities of the strip corresponding to thecontour of the control gate or more specifically the shaping blade isdesignated by the letter W in the figure.

Any metal powder suitable for the fabrication of metal strip bycompacting may be used in practicing the present invention. Metal andalloy powders as, for example, copper, iron, brass, lead, bronze,stainless steel may be used. Such metal powders have been found tocompact readily, particularly when in a fineness preferably belowIOO-mesh sieve size. Where the properties of the strip are not tooexacting as in the fabrication of some types of porous metallic filters,the strip may be made from powders of considerably larger particle sizesup to 30-mesh sieve size.

After compacting in the rolls, the green strip is normally sintered byheat to develop strength and finally the strip is usually re-rolled tomeet any desired surface and thickness specifications. While theoperations subsequent to compacting will quantitively modify thepermeability, porosity, or density of the green strip, the initialcontrol of these properties derived by virtue of the progressivethickening herein disclosed in conjunction with the production of thegreen strip is substantially preserved throughout the completeprocessing cycle. In other words, the usual processing steps subsequentto roll compacting of the loose metal powder do not adversely affect thecontrol of permeability initially provided by the progressive thickeningstep herein disclosed.

Accordingly, where it is desired that strip have more uniformpermeability and related properties laterally outwards from the centerof the strip, the loose metal powder is passed under a shaped controlgate, the lower extremity of which is in the shape of a depending archor of arcuate configuration so that after passage of the loose metalpowder thereunder the layer of powder produced will have a correspondingvariable thickness which is progressively greater on both sides of thecenter of the powder layer.

Although the gradual and progressive increase in thickness from thecenter along the width of the strip formed by passage of the powderlayer through the contoured 4 control gate is generally effective forreducing the usual variation in permeability and other properties, it isapparent that the degree of blade curvature defining the layer-formingaperture must be taken into consideration. Other factors determined byparticular conditions of actual operation must also be consideredincluding (a) the kind and particle size of the metal powder being used,.(b) the width and thickness of the strip to be produced, ('0) theinitial compacting pressure and (d) the feed rate of powder to therolls. Variation of one or more of these factors or conditions willalter the degree of contouring required which is conducive to optimumresults.

By changing the distribution of the powder fed into the mill, thetypical permeability distribution of high permeability at the edges andlow permeability'in the center of the strip can be changed to moreuniform permeability distribution. If desired, the relationship mayactually be reversed to eifect a higher permeability at or near thecenter compared to the edges of the strip by increasing the flow ofpowder toward the edges to the extent required. Changing the gateopening has a pronounced effect on the average permeability of the stripirrespective of the contouring. It will thus be seen that the gate mustbe adjusted to the opening corresponding to the desired averagepermeability level. The contouring may then be utilized to control thedistribution of permeability across the width of the strip in accordancetherewith.

It has been found that the bottom curvature of the blade for effectingthe desired distribution of powder may be varied depending uponconditions met in actual operation. In the production, for example, ofstrip of final thickness values ranging from .010 to .125 inch, acontoured gate which provides an opening which is about & to A inchwider at the edge than in the center may be advantageously employed.Dependent upon the width of the strip to be made and the permeabilitygradient desired, etc. it will be readily apparent that blade curvatures providing somewhat larger or smaller difierences in the height ofthe metal layer (h value) may be used. In general, quite satisfactoryresults have been obtained in practice with the use of curved gatesproviding an opening at the outer edge which is between 7 to inch largerthan at the center of the gate.

The control of powder distribution indicated by the data in Table I wasdetermined by attaching small chutes to the bottom of the feed trough orramp. Each of these chutes was arranged to collect the powder from onequarter of the width of the trough. The distribution was determined forone setting of the control gate opening using (a) a straight edge gate,(b) a inch curved edge gate and (c) a inch curved edge gate.

TABLE I.-FLOW DISTRIBUTION AT EXIT END 1 Left outside, left center,right center, right outside.

i "It white headdress the data that the larger opening zittlfu: edges'ofgates Hand III results'ina highertlow Percent OniOO mesh V .5 Through100 mesh, on 140. mesh v..-.. 25.6 Throughv 140 mesh, on. 200. mesh 33.4Through 200 mesh, on 3.25tmesh. -..22.5 Through 325 mesh 18.O

Stainless steelpowder was passed through a control gate equipped with ainch .curvedhlade providing a metal powder layer varying in thicknessfrom the center to its width extremities. Y I

The gate opening was set t'o'an index reading .of 33 2 corresponding toa powder flow r'at'e' of approximately 3050 grams per minute.-Thepowderlayer was-rolled to form green-strip-from--which was cut apiece-8% inches long and 4 A incheswide which was subsequently sintered.The sintered piece had a thickness of .032 inch. Sectional distributionof permeabilityacross the-width of the sintered strip was determined bymeasuring the per- 'meability coeflicient of each of four sections inaccordance with conventional permeability evaluation procedures. Thefour sections ran along 7% inches of the length of the strip and covereda width of inch each starting about a inch from the outside edge of thestrip. The four sections together, therefore, covered 3% inches or about77% of the entire width. The results are summarized below:

Green strip was prepared following the same procedure used in thepreceding example with the exception that a inch curved edge waspositioned in the control gate and the gate setting was decreased to 3corresponding to a powder flow rate of approximately 2200 grams perminute. The green strip obtained upon rolling was sintered to yieldstrip of .034 inch uniform thickness. The permeability data obtained onstrip sections corresponding to those in the previous example are listedbelow:

Percent Flow, Cu. Diff. in.

In./Sq. Perme- Perme- In./Sec. ability ability Position of Section underCoeflicient Coeflieient 50 p.s.i. in Sq. In Between Pagssflure XlO-Outsade Center Example 111 In another run varying from the precedingexample I Percent l .Flow, Cu. Diff. in. In./Sq. Perme- Perme- In./See.ability ability Posltionoisection under Coeificient Coeiiicient;

50-p.s.i. inSq. Between Pressure XlO-" Outside ,Difi. and

Center Example IV For comparison purposes, strips were rolled usingacontrol gate having an uncontoured lower edge i.e. a straight edgeblade. In a typical run thegreenstrip was formed by passing the materialthrough the rolling .mill and the resultingproduct was sintered as inthe preceding examples. A sintered. strip having a uniform thickness of.036 inch wasobtained. The measurement of permeability distribution, onquarter sections similarly ;cut, from the original strip yielded thefollowing values:

Percent Flow, Cu. Difi. in. In./Sq. Perme- Perme- In./Sec. abilityability Position of Section under Coefficient Coeflicient 50 p.s.i. inSq. In. Between Pressure X10 Outside Difi. and

Center g l as. 7 1. a 4. o 5

It will be seen from the foregoing examples that the permeabilitydistribution across the width of the strip is markedly improved byvirtue of the control of powder distribution provided by the use of acontoured control gate.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It will be readilyapparent to those skilled in the art, for example that it is possible toroll a strip having a lateral gradient of permeability from one edge tothe other by a suitable choice of the curvature of the blade. Then too,the control of powder distribution may be exercised by the use ofcontrol gates of a design other than the curved edge type hereindescribed in detail. A serrated blade for the use of multiple chutescapable of supplying variable amounts of the powder in the amountsrequired to effect the desired powder distribution'may be incorporatedin the process. It is also apparent that a moving belt arrangement couldbe used in lieu of the stationary structure shown which utilizes thegravity feeding principle. The arrangement and special relationshipbetween the feed trough and the rolls may also be varied. By way ofillustration, instead of rolling the powder in a rolling mill havingrolls which are arranged vertically above each other as shown in Fig. 1,the rolling operation may be carried out in a mill having its rollsarranged horizontally side by side with the amounts of powder fedbetween the rolls being varied across the width of the strip.

It is therefore to be understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed.

What is claimed is:

1. In the process for making strip from metal powder wherein a layer ofloose metal powder is compacted between rolls to produce green strip,the step of forming the loose powder layer to provide a progressiveincrease in thickness fror'nthe center to the lateral extremities acrossthe width thereof prior to feeding said layer to the rolls.

2. The process wherein strip is made from metal powder comprising thesteps of contouring loose metal powder to provide a layer ofprogressively increasing thickness from the center across the widththereof, and thereafter roll compacting the layer of contoured loosemetal powder in the absence of lateral support therefor to form greenstrip of modified permeability distribution characteristics compared tostrip made by compacting loose metal powder of uniform thickness acrossits width.

3. The process of claim 2 wherein the progressively increasing thicknessfor a strip at least 4 inches in width is between 3& and A of an inch atthe extremities thereof relative to the thickness at the center.

4. The process of claim 2 wherein the progressively increasing thicknessfor a strip at least 2 inches in width is from 1, to A of an inch at theextremities thereof relative to the thickness of the center portion.

5. The process wherein a strip is produced from metal powder comprisingthe steps of forming a continuous layer of loose metal powder having aconcave upper surface whereby the distribution of said powder isprogressively increased from the center across the width of said layer,compacting said concaved layer while the same is laterally unsupportedwith respect to its width dimension and thereafter sintering the greenstrip produced thereby.

6. The process of claim 5 wherein the progressive increase in thedistribution of powder from the center to the extremities across thewidth of the layer is sufiicient to effect a substantially more uniformpermeability across the width of the: processed strip by comparison withsimilarly processed strip excepting that a layer of uniform thicknessacross its width is used. 7. The process wherein a strip is producedfrom metal powder comprising contouring a layer of loose metal powder toprovide a progressively increasing thickness from the center'of themetal powder layer to the width extremities thereof, and thereaftercompacting the layer of loose metal powder in the absence of lateralconfinement of the layer with respect to its width dimension.

References Cited in the file of this patent UNITED STATES PATENTS476,706 Van Oostrum June 7, 1892 1,510,745 Montgomery Oct. 7, 19242,134,366 Hardy Oct. 25, 1938 2,332,746 Olt Oct. 26, 1943 2,350,971Pecker et al June 6, 1944 2,746,741 Naeser May 22, 1956 2,771,637Silvasy et a1 Nov. 27, 1956 2,851,354 Scanlan Sept. 9, 1958 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 937 942 May24 1960 Fritz V Lenel It is hereby certified that error appears inthe-printed specification of the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 3, line 6, for "layer 10" read layer 19 =-3 column 6, line 54 for"blade for" read blade or Signed and sealed this 15th day of November19606 S EAL) Attest:

KARL H. AXLINE Attesting Oflicer ROBERT C. WATSON Commissioner ofPatents UNITED STATESPATENT OFFICE CERTIFICATE UF CGRRECTTN Paiens Noe 2937 942 May 24 1960 Fritz Lenel It is herebfi certified that errorappears in the-printed specification oi the above "numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3 line 6 for "layer 10" read layer 19 eelumn 6 line 54 for "bladefor" read blade or -=-a Signed and sealed this 15th day of November1960,

(SEAL) Attest:

KARL He AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. IN THE PROCESS FOR MAKING STRIP FROM METAL POWDER WHEREIN A LAYER OFLOOSE METAL POWDER IS COMPACTED BETWEEN ROLLS TO PRODUCE GREEN STRIP,THE STEP OF FORMING THE LOOSE POWDER LAYER TO PROVIDE A PROGRESSIVEINCREASE IN THICKNESS FROM THE CENTER TO THE LATERAL EXTREMITIES ACROSSTHE WIDTH THEREOF PRIOR TO FEEDING SAID LAYER TO THE ROLLS.